Viral diseases - avian encephalomyelitis, Biology

Viral Diseases

Avian encephalomyelitis

This is enterovirus disease of chicken, pheasants, turkeys and Japanese quails caused by the member of the family Picornaviridae. It causes inapparent infection or drops in egg production in adult layer birds, whereas in young chicks, it is responsible for epidemic tremors. There are 15 serotypes of the virus which are enterotopic in nature which differ in their neurotropism and virulence. The morbidity and mortality varies depending on the immune status of the birds. The disease is transmitted vertically through infected eggs or horizontally by ingestion of contaminated food and water. The virus is resistant to environmental conditions particularly if protected by organic matter.

Symptoms and lesions: In layers, the drop in egg production is very low (5-10%) and of short duration (less than 2 weeks). In breeders there may be a drop in hatchability of about 5%, but there is serious disease in the progeny involving central nervous system. The clinical signs include dullness, ataxia and tremors of the head and neck followed by paralysis, prostration and death. The mortality may reach upto 25%. Unilateral or bilateral blindness or corneal opacity may also be seen. There may not be any gross lesions seen during PM examination. In central nervous system, the inflammatory lesions are noticed in brain and ganglions however, peripheral nerves are not affected.